Firefox 4 has finally been released, and while it looks an awful lot like Opera, there’s no question that it’s faster, better, and an all-around great upgrade from 3.6. Here’s a couple of highlights.

The bottom line? If you use a ton of add-ons, you’re going to want to check them out before you upgrade, to make sure they are compatible. Firefox 4 changes the underlying extension architecture a great deal, and many add-ons just won’t work.

What’s New in Firefox 4.0

There’s a ton of new stuff in Firefox 4, especially behind the scenes. Here’s a couple of key changes:

New Interface that Looks Like Opera – The new Firefox interface is a huge improvement, but it does borrow some elements heavily from the Opera browser, especially the menu in the upper left.

Hardware Acceleration – Looks like everybody is implementing this now, since Microsoft put it into IE9, and it makes Firefox much, much faster.

New Add-ons Panel – you can now browse the add-ons through a very nice add-ons panel, built right in.

Internal Add-ons Changes – which break many of the add-ons out there. You’ll probably find that add-on compatibility isn’t as good, and even if you hacked Firefox to use the old add-ons, many of them won’t work well.

There’s a ton of other features, but you can always download and check it out.

Firefox Shows Up Late to the Party, Wearing the Same Opera Clothes

Yeah, we’re being a little hard on Firefox here—but it really does look like the Opera web browser. Click the screenshot for a larger view.

All I did was hide the Opera status bar (somebody please call Opera and tell them the status bar is dead), and remove a button or two.

The Menus Have Moved

If you’ve ever used Opera, you’ll see that Firefox now has the exact same style of menu, up in the upper left. It’s from here that you can get to things like the Add-ons, Options, and everything else.

Pinning App Tabs

If you’ve ever used Google Chrome, you’re familiar with the application tabs, which only show you an icon. They are now baked directly into Firefox instead of requiring an add-on. Definitely a good change.

Enabling Windows 7 Taskbar Previews

If you head into the Options panel, you can select the “Show tab previews in the Windows taskbar” option…

…which will show every tab as a separate window when you mouse over the taskbar icon. You can mouse over the tab, and Aero Peek will show a full-size preview of it.

Bringing the Menus Back

The menu bar is hidden by default, but if you hit the Alt key, it’ll show up temporarily—or you can just use one of the shortcut keys directly. Using Alt+F, for example, will bring up the File menu.

Private Browsing

Firefox has private browsing, which you can access from the Firefox menu on the upper left—the only problem is that it replaces your current session entirely—so if you had tabs open, they will be temporarily closed.

This is probably the one feature where Firefox could use some improvement—Google Chrome and IE have much nicer private browsing modes.

Tab Groups

If you hit Ctrl+Shift+E or use the little tab menu on the right of the tab bar, you can drag and drop to rearrange your open tabs into groups. It takes a little bit to get used to, but it’s an interesting way to manage loads of tabs.

All in all, you should still switch to Firefox 4, it’s blazing fast, and a huge improvement.